When battling Darkhammers (for example, the three in the last room of the Cave of Ordeals), throw bombs. This takes their armor off quickly. Once all of it is off, it will dodge if you throw bombs. To kill it with the armor off, get close enough until it tries to hit you. Just before it hits you, roll out of the way to get in back of it. Then, just start slashing it with your sword.